Herpes simplex virus type 1 (HSV-1) establishes lifelong latent infections in sensory neurons. Reactivation of latent HSV-1 in neurons of the trigeminal ganglion (TG) can lead to retrograde transport to the brain and cause HSV encephalitis, which is the leading cause of sporadic infectious encephalitis in the United States. Anterograde transport of reactivated HSV-1 from the TG leads to orofacial and ocular lesions, with infections of the cornea representing a leading infectious cause of blindness worldwide. Understanding and exploiting mechanisms responsible for maintaining HSV-1 in a latent state might represent the most promising approach to preventing these devastating diseases. Emerging evidence in both mouse models and humans suggests a role for HSV-specific CDS T cells in maintaining HSV-1 latency in infected TG. However, prudence dictates that exploitation of a mechanism with the potential cellular lethality of CDS T cells for neurons should be approached with caution and a thorough understanding of the effector mechanisms CDS T cells employ in preventing HSV-1 reactivation from latency in neurons. The proposed studies will test our hypothesis that CDS T cells prevent HSV-1 reactivation from neuronal latency in part through interferon-y secretion and in part through a non-lytic function of their lytic granules. In Specific Aim 1, we will compare the capacity of HSV-specific CDS T cells expanded from the latently infected TG of wild type mice and mice deficient in the lytic granule components perforin and granzyme B to inhibit HSV-1 reactivation from latency in ex vivo cultures of CDS-depleted latently infected wild type TG;we will provide initial evidence that wild type CDS T cells prevent HSV-1 reactivation from latency without destroying the neurons;and explore possible mechanisms by which granzyme B might intervene directly in the viral reactivation process. In Specific aim 2 using a combination of live- and fixed-cell fluorescence microscopy, we will directly observe the interaction between HSV-specific CDS T cells and latently infected neurons;characterize the nature of the neuroimmune synapse;determine if synapse formation leads to directed release of lytic granules, and determine if lytic granule release leads to activation of the apoptotic machinery of the neuron. HSV-1 infection is generally acquired early in life and affects the majority of the world's population by middle age. Prophylactic antiviral therapy can reduce the rate of recurrence of herpetic disease;however, this treatment is not curative, and it only acts once the virus has reactivated from latency. Therefore, understanding the protective immune response to latent HSV-1 neuronal infection in hopes of developing an immune-based therapeutic vaccine to inhibit HSV-1 reactivation is an important global public health issue.